Basically, parliament and funkadelic are the same group of musicians. However, they released more rock oriented albums under the name funkadelic, and they also released more funk oriented albums under the name parliament. The hyphenated Parliament-Funkadelic term (P-Funk for short) is used to group all that music as a whole.

There was a bigger difference between Funkadelic and Parliament in the beginning, but they started sounding more like each other towards the late-70s. They also started playing live as just "Parliament-Funkadelic" by the mid-70s.

George Clinton started calling the band P-Funk All Stars in the 1980s due to legal issues. It's been the name of the band for almost 30 years now (considerably longer than what the two names they were using before that and are best known for). Sure, it's been used mostly for live performances as Clinton has put out most of his recorded work under his own name ever since.

If it has horns it's probably Parliament. If it has wailing lead guitar it's probably Funkadelic.

There were no members besides Clinton and Gary Shider that were there through the whole thing but if both bands made a record in the same year it probably had most of the same lineup.

The very earliest Parliament album, Osmium, is pretty much identical to the early Funkadelic albums, and has some of my favorite stuff of theirs on it. I Call My Baby Pussycat = STOMPER. And they were doing R&B stuff as early as the 50s under the name The Parliaments. But once you're into the seventies, the easiest way to tell the difference is to listen for that lead guitar.